Michigan Sen. Carl Levin says tests are being conducted on a suspicious letter that was delivered to his Saginaw office and the staffer who discovered the letter is spending the night at a local hospital as a precaution.

A hazmat team was called to Levin's Saginaw office, located at 515 N. Washington Avenue on Wednesday morning.

About two hours after the hazmat team was called in, agents from the FBI showed up to investigate.

An FBI spokesperson tells TV5 it's still too early to talk about the contents of the suspicious letter found at the office.

The building that houses the Senator's office used to be known as the Delphi Tower. Hazmat officials arrived around 11 a.m. and departed from the scene around 2 p.m. The building also contains offices for Saginaw Future.

"Law enforcement officials are performing tests on the suspicious letter that was delivered to my Saginaw office," said Levin in a statement Wednesday afternoon. "We do not expect to learn at least a preliminary result of those tests until late tonight or tomorrow. The staffer who discovered the letter is being kept overnight at a local hospital for precautionary reasons, but has no symptoms. We do not know yet if the letter has any connection to suspicious mail sent to other public officials. I want to repeat how grateful I am to local, state and federal authorities who reacted so quickly and professionally, and especially to my Saginaw staff for being so vigilant.

People were allowed back into the building around 2:30 p.m., but not allowed on the fourth floor.

"The staffer who discovered the letter is being kept overnight at a local hospital for precautionary reasons, but has no symptoms," Levin continued in the statement. "We do not know yet if the letter has any connection to suspicious mail sent to other public officials. I want to repeat how grateful I am to local, state and federal authorities who reacted so quickly and professionally, and especially to my Saginaw staff for being so vigilant."

TV5 is waiting to hear from the FBI as to what was discovered inside the letter and envelope.

Levin said his Saginaw office would remain closed until further notice. Anyone seeking to contact that office is asked to call the senator's Detroit office at 313-229-6020.

WNEM will continue to follow this story and will provide updates as more information is learned.

All this is happening on a day when the FBI says the letters sent to President Barack Obama and Sen. Roger Wicker are related and are both postmarked out of Memphis, Tenn., dated April 8.

In an intelligence bulletin obtained by The Associated Press, the FBI says the letters both say: "To see a wrong and not expose it, is to become a silent partner to its continuance." Both letters are signed, "I am KC and I approve this message."

The FBI says the substance in both letters have preliminarily tested positive for ricin, a potentially fatal poison.

Both the letters to Wicker, R-Miss., and to Obama were intercepted at off-site mail facilities.

The FBI says it is pursuing investigative leads to determine who sent the letters.